THE BIG SURPRISE in the Persian Gulf war has been the failure of Iraq to polish off Iran. Iraq had been widely conceded a role as the coming regional Prussia. Iran, its American connection lost and its armed forces wracked by revolution, was supposed to be a pushover. But though Iraq had the aggressor's advantage of surprise, it failed to achieve the rapid victory that seems to have been central psychologically, politically and logistically to its strategy. Meanwhile, the Tehran regime has put its American training and equipment to use and has waved the national flag. It may also be that, notwithstanding Iraq's attempt to subvert Iran's Arab minority, Iran has an even more potent ethnic card available in its appeal to Iraq's Shiite Moslem majority. Whatever the full explanation, the war goes raggedly on. The outcome may be harder to score than anyone expected.

This newly perceived condition of uncertainty has at least two major implications for states outside the region. It prolongs the period of risk in which the war could overflow the boundaries of Iraq and Iran and effect the flow of oil. This is bound to ensure continuing -- and continuingly frustrating -- international efforts to dampen the violence and keep open the Strait of Hormuz.

It also creates something more of an opening, though hardly a clear path, for the diplomacy of outsiders. The longer the war, for instance, presumably, the greater will be the combatants' need for spare parts -- Iraq must go to Moscow, Iran to Washington. And the longer the war, the more hesitant outsiders will be to cultivate one party as the likely winner. This will tend to work against Iraq, which, before the war, enjoyed a putative ascendancy. A larger place may have to be left for Iran, with three times Iraq's population the largest state in the Gulf.

The United States entered this crisis without the influence in or on either combatant state to see to its several interests of calming the region down and reclaiming the hostages. Not much has changed. Even if Iran were to suggest a spare-parts-for-hostages deal, the administration would still have to consider the reaction of Arabs with whom the United States has important ties. Such public diplomacy, anyway, as the administration has in motion, focusing on appeals for a cease-fire and planning for a naval force in the Strait of Hormuz, appears to be mostly an exercise in collective hand-wringing.Perhaps the best course in the crisis is merely to make a virtue of necessity and avoid rash acts.